The invention relates to plasters containing active substances, comprising a backing material and, applied thereon, a hot-melt self-adhesive composition which comprises the active substance or, if appropriate, two or more active substances that are delivered to the skin.
Transdermal therapeutic systems (TTS) are forms of administration of medicaments which deliver one or more medicaments to the skin over a defined period at their site of use. A distinction is made here between systemic and local administration forms. With systemic administration forms, the active substance passes through the skin into the blood circulation by diffusion and can act within the body as a whole. Local administration forms, on the other hand, act only at the sites of application. The active substance remains in the skin or in the underlying layers.
Numerous embodiments of such plasters have already been described, some of which operate in accordance with the reservoir principle, where the active substance is delivered, for example, by way of a membrane, in some cases also with a matrix system or with a more complex multilayer structure.
It is also known that the adhesive composition of the plaster can be employed as the matrix containing active substance. In addition to self-adhesive compositions applied from solution, hot-melt self-adhesive compositions have also been proposed for this purpose, for example in EP-A 663 431, EP-A 452 034, EP-A 305 757, DE-A 43 10 012, DE-A 42 22 334 and DE-C 42 24 325.
The active substance listed in these cases, if at all, have been systemic ones.
Active substance plasters which promote the circulation belong to the group of local therapeutic systems. The use of such plasters is indicated for treating rheumatic complaints, sciatica, lumbago, stiff neck, shoulder/arm pain and muscular strains and sprains, muscular aching or muscle, joint and nerve pain in the region of the locomotor system.
Capsaicin, belladonna and nonivamide are known active substances in such local, circulation-promoting plasters. Because of their use on the motility apparatus they are in general required to adhere strongly. Usually, the plasters are coated over their full area with a resin-rubber adhesive composition which comprises the active substance.
However, plasters of this kind, which usually have to be applied over a relatively large area, exhibit in some cases distinct mechanical skin irritations after removal in the case of sensitive patients. In some cases there are allergic reactions. After a prolonged period of wear, their removal is to some extent painful.
A further disadvantage of the known thermally active plasters with an adhesive composition based on natural rubber which is applied in the form of a solution with organic solvents to the plaster backing is the comparatively low rate of release of the active substance.
The object of the invention, therefore, was to develop circulation-promoting (hyperaemic) and thus thermally active plasters which should feature good activity, i.e. a relatively high rate of release, and good skin compatibility at the same time as having good adhesion. In addition, they should be able to be prepared with little technical complexity and in an environmentally compatible manner.
This object is achieved by active substance-containing plasters according to claim 1.
It has been found that hot-melt self-adhesive compositions are also suitable for the release of substances having a hyperaemic action and just a local action.
These active substances are primarily the known substances of cayenne pepper and also the synthetic capsacinoid NVA (nonivamide), and also nicotinic acid derivatives, preferably benzyl nicotinate or propyl nicotinate.
The concentrations are from 0.01 to about 20% by weight, preferably from 0.1 to 10% by weight.
With particular preference, the hot-melt adhesive compositions are based on synthetic thermoplastic polymers, such as synthetic rubbers, especially block copolymers, polyacrylates, polyurethanes, polyesters, polyolefins, polyacrylamides or silicones.
For systems with particularly strong adhesion the adhesive composition is based preferably on block copolymers, especially A-B or A-B-A block copolymers or mixtures thereof. The hard phase A is ideally polystyrene or its derivatives and the soft phase B comprises ethylene, propylene, butylene, butadiene, isoprene or mixtures thereof, with particular preference being given to ethylene and butylene or mixtures thereof.
Polystyrene blocks can also, however, be present in the soft phase B, in amounts of up to 20% by weight. The overall proportion of styrene, however, should always be less than 35% by weight. Preference is given to proportions of styrene of between 5% and 30%, since a lower proportion of styrene makes the adhesive composition more conformable.
The tailored blending of diblock and triblock copolymers is particularly advantageous, with preference being given to a proportion of diblock copolymers of less than 80% by weight.
In an advantageous embodiment the hot-melt pressure-sensitive adhesive composition has the following composition:
from 10 to 90% by weight of block copolymers,
from 5 to 80% by weight of tackifiers, such as oils, waxes, resins or mixtures thereof, preferably mixtures of resin and oils,
less than 60% of plasticizers
less than 15% by weight of additives
less than 5% by weight of stabilizers.
In a particularly preferred embodiment of an adhesive composition of this kind which is additionally provided with the hyperaemic active substance, the adhesive composition is based on an A-B/A-B-A block copolymer of styrene, ethylene and butylene having a styrene content of less than 35% by weight, and contains 0.1-10% by weight of nonivamide, preferably about 0.2% by weight.
Tackifiers used are the hydrocarbon oils, hydrocarbon waxes and hydrocarbon resins. In this context the oils, such as paraffinic hydrocarbon oils, or waxes, such as paraffinic hydrocarbon waxes, have a favourable effect on bonding to the skin owing to their consistency. Plasticizers used are long-chain fatty acids and/or their esters. These additives serve to adjust the adhesion properties and the stability. The addition of mineral fillers in minor amounts is also possible.
The adhesive compositions are adjusted such that at a frequency of 0.1 rad/s they have a dynamic-complex glass transition temperature of less than +10xc2x0 C., preferably from xe2x88x923xc2x0 to xe2x88x9230xc2x0 C. and, with very particular preference, from xe2x88x926xc2x0 to xe2x88x9225xc2x0 C.
The tailored reduction in the glass transition temperature of the self-adhesive composition as a consequence of the selection of the tackifiers, the plasticizers and the polymer molecule size, and of the molecular distribution of the components employed, ensures the required bonding with the skin even at critical points of the human locomotor system, in accordance with the required function.
The high shear strength of the self-adhesive composition is achieved by the high cohesiveness of the polymer. The good finger tack is a result of the plasticizers and tackifiers employed.
The distribution of the active substances within the adhesive composition takes place in a thermal homogenizer, for example a thermal mixer, thermal kneader, roll mills or screw systems. The active substance can be added to the fully prepared adhesive composition. Alternatively, for example, the active substance can also be incorporated into an intermediate stage or into the initial mixture.
Product properties such as tack, glass transition temperature and shear stability can be quantified readily using a dynamic frequency measurement. In this case, use is made of a rheometer controlled by shearing stress. The results of this measurement method give information on the physical properties of a substance by taking into account the viscoelastic component. In this instance, at a preset constant temperature, the hot-melt pressure-sensitive adhesive is set in oscillation between two plane-parallel plates with variable frequencies and low deformation (linear viscoelastic region). Via a pickup control unit, with computer assistance, the quotient (Q=tan xcex4) between the loss modulus (Gxe2x80x3, viscous component) and the storage modulus (Gxe2x80x2, elastic component) is determined: Q=tan xcex4=Gxe2x80x3/Gxe2x80x2.
A high frequency is chosen for the subjective sensing of the tack, and a low frequency for the shear strength. A high numerical value denotes better tack and poorer shear stability.
The complex-dynamic glass transition point is the point of transition from the amorphous to the viscoelastic region. It corresponds to the maximum of the temperature function at a given frequency.
In accordance with the invention, preference is given to pressure-sensitive hot-melt adhesive compositions for which the ratio of the viscous component to the elastic component at a frequency of 100 rad/s at 25xc2x0 C. is greater than 0.7, or to pressure-sensitive hot-melt adhesive compositions where the ratio of the viscous component to the elastic component at a frequency of 0.1 rad/s at 25xc2x0 C. is less than 0.4.
The adhesive composition containing an active substance can be applied to the entire area of an appropriate conformable backing material, such as wovens, knits, films, nonwovens, paper, foam or laminates thereof, and advantageously can also be applied with areal restriction, for example by halftone printing, thermal screen printing, thermal flexographic printing or intaglio printing. This leads to particularly good air and water vapour permeability of the adhesive film.
In the case of screen printing, preference is given to application in the form of domes, especially those where the ratio of diameter to height is less than 5:1. Printed application of other forms and patterns on the backing material is also possible, for example a printed pattern in the form of alphanumeric character combinations or patterns such as matrices, stripes and zigzag lines.
In addition, the adhesive composition can also be sprayed on, for example, producing a more or less irregular applied pattern.
The self-adhesive composition can be distributed uniformly over the backing material; alternatively, it can also be applied with varying thickness or density as appropriate for the function of the product.
The principle of thermal screen printing consists in the use of a rotating, heated, seamless, drum-shaped, perforated, cylindrical screen which is fed via a nozzle with the pressure-sensitive hot-melt adhesive composition. A specially shaped nozzle lip (circular or square doctor blade) presses the self-adhesive composition, which is fed in via a channel, through the perforation of the screen wall and onto the backing web that is conveyed past it. This backing web is guided by means of a counterpressure roller against the external jacket of the heated screen drum at a rate which corresponds to the peripheral speed of the rotating screen drum.
Using this printing technique it is possible to lay down the size and shape of the domes in a defined manner. The base diameter of the domes can be chosen from 10 xcexcm to 5,000 xcexcm, the height of the domes from 20 xcexcm to about 2,000 xcexcm, preferably 50 xcexcm to 1,000 xcexcm, the low-diameter range being intended for smooth backings and the range of greater diameter and greater dome height being intended for rough or highly porous backing materials. The positioning of the domes on the backing is laid down in a defined manner by the geometry of the applicator unit, for example the gravure or screen geometry, which can be varied within wide limits. The backing material is preferably coated at a rate of more than 2 m/min, more preferably from 20 to 100 m/min, the chosen coating temperature being greater than the softening temperature of the adhesive system.
The pressure-sensitive hot-melt adhesive composition can be applied to the backing material with a weight per unit area of more than 15 g/m2, preferably between 90 g/m2 and 400 g/m2 and, with very particular preference, between 130 g/m2 and 300 g/m2.
The percentage area that is coated with the hot-melt pressure-sensitive adhesive composition should be at least 20% and can range up to about 95%, for specific products preferably from 40 to 60% and from 70% to 95%. This can be achieved, if desired, by means of multiple application, with the possible use if desired of adhesive compositions having different properties.
Depending on the backing material and on its temperature sensitivity, the self-adhesive layer can be applied directly or first applied to an auxiliary support and then transferred to the ultimate backing. Subsequent calendering of the coated product and/or pretreatment of the backing, such as corona irradiation, may be advantageous for better anchoring of the adhesive layer.
After coating, the backing material is usually covered on the adhesive side with an anti-adhesive backing material, such as siliconized paper. The plasters are then punched out in the desired size and, if desired, are sealed individually and sterilized, preferably by means of gamma rays.